System for controlling cryogenic fluid flow rate and joule-thomson effect cooler comprising same

ABSTRACT

The invention concerns a flow rate control system comprising two components ( 1, 2 ) made of materials with different expansion ratios, one of said components ( 7 ) being arranged at least partially around the first ( 1, 2 ) component so as to normally provide an annular outlet ( 13 ) which is closed when the component ( 7 ) contracts, the passage of the gas to be expanded being then limited to a passageway with reduced cross-section in the central component, for example consisting in an axial groove ( 12 ). The invention is useful for producing any type or Joule-Thomson effect cooler.

The present invention relates to cryogenic fluid flow control systems ofthe type comprising a first element forming a fluid inlet channel and anoutlet passage that can be selectively blocked off by a second elementthat can move relative to the first element by an effect due to thedifference in expansion coefficients between the materials of the firstand second elements.

Known flow control systems of this type, such as those described forexample in documents FR-A-2 377 588 or EP-A-0 170 948, comprise a needlethat can move longitudinally relative to an outlet orifice due to theeffect of axial differential expansions between the first element havingthe orifice and a moveable device that includes a rod and/or a bellowssupporting the needle, in an arrangement that is tricky to manufactureand assemble, and therefore expensive and with no guarantee ofreliability, especially in the presence of vibrations.

The object of the present invention is to propose a system of the typedefined above that is of simple, robust and inexpensive construction andis of greater reliability.

To do this, according to one aspect of the invention, the outlet passagecomprises a part extending transversely relative to the fluid inletchannel and emerging on the periphery of an end region of the firstelement, the second element being placed at least partly around this endregion.

According to more particular features of the invention:

the end region of the first element is approximately cylindrical and thesecond element is annular and coaxial with said end region;

the outlet passage includes a downstream part of reduced section thatcannot be blocked off by the second element;

this downstream part consisting of an axial groove formed in theperiphery of the end region or of a capillary tube that extends theinlet channel through the end region;

at least one of the first and second elements is made of a plastic or ametallic material.

The subject of the present invention is also a Joule-Thomson expansioncooler, especially for a cryostat, that includes such a cryogenic fluidflow control system.

Other features and advantages of the invention will become apparent fromthe following description of embodiments given by way of illustration,but implying no limitation, in conjunction with the appended drawings inwhich:

FIG. 1 is a schematic view in partial section of a first embodiment ofthe invention;

FIG. 2 is a schematic view similar to FIG. 1 of another embodiment ofthe invention; and

FIG. 3 is a partial view, in section, of a cryostat incorporating aJoule-Thomson cooler according to the invention.

In the description that follows and in the drawings, identical orsimilar elements bear the same reference numbers.

FIG. 1 shows the downstream end of one embodiment of a flow controlsystem for a cryostat with a Joule-Thomson cooler.

This system comprises a first elongate element, denoted overall by thereference 1, which terminates in an end part 2 of enlarged diameter andalong which first element there extends a blind bore 3 which selectivelycommunicates with a source 4 of pressurized gas, for example nitrogen orargon.

According to one aspect of the invention, the end part 2 forms acylindrical peripheral region 5 into which at least one radialtransverse passage 6 emerges. Placed around the cylindrical peripheralregion 5, normally loosely, is a second annular element or ring 7 heldin place, in the example shown, around the peripheral region 5 by acover 8 fitted over the end part 2 and provided with an axial orifice 9facing the end wall 10 of a casing, for example made of metal, in whichthe flow control system is mounted, the said casing carrying, forexample, an infrared detection cell 11. The ring 7 may be held in placearound the peripheral region 5 by a simple stop, of the strap or pintype inserted into the end part 2. In the embodiment shown in FIG. 1, anaxial groove 12 emerging upstream into the radial passage 6 anddownstream into the lower face of the end part 2 is formed in theperipheral region 5.

The annular ring 7 is made of a material having an expansion coefficientsubstantially higher than that of the central element 1 and so theoperation of the system is as follows:

Before injection of the gas to be expanded, that is to say at roomtemperature, an annular outlet passage 13 of cross section substantiallylarger than that of the passage 6 exists between the ring 7 and thesurface 5.

When the cryogenic fluid is injected into the bore 3, its expansion uponleaving the flow control system via the passages 6 and 13 causes rapidcooling of the entire system, resulting in contraction of the ring 7around the end part 2 and resulting in rapid disappearance of theannular outlet passage 13. Consequently, the compressed gas to beexpanded can now escape only via the axial groove 12, that is to saywith a much smaller flow rate than previously via the annular passage13, thus making it possible to ensure continuous expansion formaintaining the refrigeration of the cryostat at the cost of a smalltap-off of gas.

In the embodiment shown in FIG. 2, the gas outlet passage of small crosssection is produced by a capillary tube 13 that passes through the endwall of the end part 2, being brazed to the latter and extending intothe bore 3 forward of the radial passage 6 and advantageously beyond theopening 9 in the cover 8, in order to direct the reduced flow of coldfluid directly onto the region of the cell 11.

In the cryostat embodiment shown in FIG. 3, the flow control system issimilar to that shown in FIG. 1, but the blind hole 3, where the radialpassage 6 emerges, is offset laterally, in the end part 2, near theaxial leakage groove 12, and the working gas is conveyed by a tube 14,the downstream end of which is fitted into the bore 3 and brazedthereto, and the upstream region of said tube has the shape of a spiralin order to form a heat exchanger coil 15 extending axially into thecasing 10 of the cryostat.

For moderate gas pressures (not exceeding 200 bar), the element 1 may bemade of a plastic, for example a polyamide, and the ring 7 may be madeof a plastic, for example cavity Teflon™.

For moderated and high gas pressures, the elements 1 and 7 are made ofmetal, advantageously Invar and aluminum respectively. The ring 7 mayalso be made of copper or a copper alloy.

Although the invention has been described in relation to particularembodiments, it is not limited thereby but is capable of modificationsand variants that will become apparent to a person skilled in the artwithin the context of the claims appended hereto. In particular, theinvention may apply in any type of Joule-Thomson geometry, for exampleone that is conical or flat.

1-8. (canceled)
 9. A cryogenic fluid flow control system apparatus,comprising: a) a first element, wherein said first element comprises anend part with a periphery, and wherein said first element forms a fluidinlet channel and an outlet passage; and b) a second element, that canmove relative to the first element by an effect due to the difference inexpansion coefficients between the materials of the first and secondelements, thereby selectively blocking off the outlet passage with thesecond element, wherein the outlet passage comprises a part extendingtransversely relative to the inlet channel and emerging on the peripheryof the end part of the first element, with the second element beingplaced at least partly around said end part.
 10. The apparatus of claim9, wherein said end part is approximately cylindrical and said secondelement is annular and coaxial with said end part.
 11. The apparatus ofclaim 9, wherein said outlet passage further comprises a second part ofreduced section that cannot be blocked off by said second element. 12.The apparatus of claim 11, wherein said second part of the outletpassage further comprises an axial groove formed in said periphery ofthe end part of the first element.
 13. The apparatus of claim 11,wherein said second part of the outlet passage is formed by a capillarytube that extends the inlet channel through the end part of the firstelement.
 14. The apparatus of claim 9, wherein at least one of saidfirst and second elements comprises a plastic.
 15. The apparatus ofclaim 9, wherein at least one of said first and second elementscomprises a metallic material.
 16. A Joule-Thomson cooler apparatuscomprising a flow control system, wherein said flow control systemcomprises: a) a first element, wherein said first element comprises anend part with a periphery, and wherein said first element forms a fluidinlet channel and an outlet passage; and b) a second element, that canmove relative to the first element by an effect due to the difference inexpansion coefficients between the materials of the first and secondelements, thereby selectively blocking off the outlet passage with thesecond element, wherein the outlet passage comprises a part extendingtransversely relative to the inlet channel and emerging on the peripheryof the end part of the first element, with the second element beingplaced at least partly around said end part.